On Tuesday she was freed on a $5 million bail and ordered to remain at her parents' home, and not make contact with any members of the group.

Ahead of the hearing Business Insider reported that the Smallville star attempted multiple times to recruit Watson to join NXIVM – an invite-only group of women who were allegedly pressured into starving themselves and having sex with Keith Raniere, the group’s leader.

Mack repeatedly attempted to approach the British actress via Twitter in 2016, asking her to consider joining a "women's movement."

She did not manage to make contact with Watson, however, as she used a wrong Twitter account.

In January 2016, she tweeted: “@EmWatson I'm a fellow actress like yourself & involved in an amazing women's movement I think you'd dig. I'd love to chat if you're open.”

The account appears not to exist - unlike the @EmmaWatson account, which has almost 30 million followers.

A month later she tried again, tweeting: “@EmWatson I participate in a unique human development & women's movement I'd love to tell you about. As a fellow actress I can relate so well to your vision and what you want to see in the world. I think we could work together. Let me know if you're willing to chat.”

She tried for a third time in March, on International Womens’ Day: “@TheCathyJensen @EmWatson Thank you for the bump up! Would love to chat with a fellow change-maker! #InternationalWomensDay”

Richard Donoghue, the US attorney for the Eastern District of New York, said in a statement: "As alleged in the indictment, Allison Mack recruited women to join what was purported to be a female mentorship group that was, in fact, created and led by Keith Raniere.

Allison Mack, pictured in 2012Credit: GUS RUELAS/REUTERS

"The victims were then exploited, both sexually and for their labor, to the defendants' benefit."

Mack gave an interview to Fine magazine in March 2017, praising Raniere for helping her when Smallville ended after 10 seasons in 2011.

"I was 28 and I felt not quite sure where I was going or who I was,” she said.

“I think that was probably the most bumpy transition."

Asked how she managed to navigate that change in her life, she said: "I have a wonderful teacher and mentor named Keith Raniere, who really gave me some incredible guidance."

Raniere is believed to have run NXIVM since 2003, from a base in Albany, New York.

Court documents allege that he "maintained a rotating group of fifteen to twenty women with whom he maintains sexual relationships.

“These women are not permitted to have sexual relationships with anyone but Raniere or to discuss with others their relationship with Raniere.

“Some of the Nxivm curriculum included teachings about the need for men to have multiple sexual partners and the need for women to be monogamous."

The women were also submitted to a branding ritual, in which a symbol integrating Raniere's initials was seared into their skin near their pubic region, the complaint further alleged.

It is claimed that the organisation operated as a pyramid scheme, with women paying for classes to rise up the ranks and recruiting new members to progress up the hierarchy.